Process for the production of hydrogen fluoride and calcium sulphate



C. B. PROCESS FOR HAYwoRTH ETAL 3,160,473 THE PRODUCTION OF HYDROGEN l FLUORIDE AND CALCIUM SULPHATE Filed April 27. 1961 Dec.` 8, 1964 INVENTORS: CURTIS B.HAYWORTH ROBERT H. HUTZLER AUBREY W. MICHENER,JR. RICHARD SOBEL AT ORNEY United States Patent Q 3,160,473 PROCESSFOR THE PRUEUCHGN @F HYDRQG-EN FLUORIDE AND CALCEUM SULPHATE Curtis B. Hayworth, Morristown, NJ., Robert H. Hutzler, Wilmington, Del., Aubrey W. Michener, Jr., Rockaway Borough, NJ., and Richard Sobel, Claymcnt, Del., assignors to Allied Chemical Corporation, New York, NX., a corporation of New York Filed Apr. 27, 1961, Ser. No. 105,992 4 Claims. (Cl. 23-153) This invention relates to the manufacture of hydrogen fluoride and more particularly refers to a new and improved process for the production o f hydrogen fluoride by reaction of iiuorspar (calcium uoride) with sulfuric acid.

Y For the past 30 or more years commercial production of hydrogen fluoride has been carried out by introducing fluorspar and sulfuric acid into an externally tired rotary kiln wherein the sulfuric acid reacts with the calcium fluoride to produce hydrogen fluoride and calcium sulfate. The evolved HF gas containing SO2 and elemental sulfur as contaminants is withdrawn from the kiln and subjected to conventional purification by cooling, acid scrubbing, rectifying and stripping operations. A problem which plagued facture of hydrofluoric acid has been the formation of hard lumps in the kiln as the reaction between the sulfuric acid and the spar proceeds thus decreasing the efiiciency of heat transfer from the furnace shell to the reactants and materially reducing the capacity of the unit. Many years ago, U.S. Patent 1,748,735 of February 25, 1930, in order to counteract this situation, the expedient was adopted of inserting a number of heavy steel rails, sections of railroad rails of a length approximately equal to the interior longitudinal dimension of the kiln and weighing about 25 pounds per foot. These rails are tumbled freely in the bed by special lifters falling with considerable force (lighter rails were found unsatisfactory) and tend to break up the lumps as they develop. As can be appreciated the wear and tear and maintenance on the equipment due -to the tumbling of these heavy rails is considerable and represents an appreciable item in the cost of operation. Nevestheless, the art knew no better method of operation and for decades practiced this procedure. Recently, Du Pont Patent 2,846,290 of August-5, 1958, in attempting to overcome the problem of lump formation long existing in the art suggested carrying out the reaction in the presence of chlorinated benzene as a diluent. vThis procedure has the drawbacks of requiring the use of large -amounts of an expensive diluent, chlorinated benzene, contamination of the product, expansive procedurefor removal of the chlorinated benzene as well as heat loss attendant its use.

An object of the present invention is` to provide a method for reacting sulfuric acid and fluorspar to produce hydrogen uoride Without lamp formation.

A further object is to provide a more eiiicient method for-.producing hydro-gen iiuoride by reaction of uor'spar and sulfuric acid with increased plant capacity and lower maintenance cost.

A still further object is to provide a method for reacting` fluorspar and sulfuric acid to produce hydrogen iiuoride containing appreciably reduced amount of conj taminants.

Other objects and advantages will be apparent from the following description and accompanying drawing.

In accordance v.with the present invention fluorspar and sulfuric acid are converted to hydrogen uoride without lumpformation, with purer hydrogen fluoride and-with increased plant capacity by calcining the uorspar at a temperaturewithin the range of about 80()1300V F.,

the art in the commercialmanul give 3,160,473 Patented Dec. 8, 1964v ice preferablyrwithin the range of 900-1l00 F., passing the heated, calcined lluorspar into an externally heated reaction zone, introducing sulfuric acid having a concentration of about 95-l00% H2804, preferably 99-100% H2804, preferably at a temperature Within the range of 200-350" F., in at least stoichiometric amount for reaction, with the iluorspar, preferably in small stoichiometric excess of up to 20%, maintaining the reaction mixture v-in the reaction zone at a temperature within the range ofy 30G-600 F., preferably within the range of G-450 F., eifect reaction of the iluorspar toV produce hydrogen uoride and calcium sulfate, releasing evolved hydrogen fluoride from the reaction zone and discharging calcium sulfate from the reaction zone.

'In the course of our investigation we discovered that precalcination of the uorspar at a high` temperature within the range of about 800-1300 F. caused some change such that when the heated calcineduorsparwas introduced into the kiln together with sulfuric acid for the production of hydrogen uoride, lump formation was eliminated Yand it was no longer necessary'to employ heavy steel rails, and furthermore, we obtained more efiicient heat transfer in the kiln and the kiln operated at an increased capacity up to 50%. We do not know what physical or chemical changes in the properties in the uorspar occur at the high temperature calcination but have noted the radical improvements resulting from such calcination. Temperature of calcination is important and should be within lthe range of about 800-1300 F., as temperatures materially below this range `do not satisfactory results. Another important advantage resulting from the high temperature calcination of the uorspar is the elimination of an appreciable amount of naturally occurring impurities .in the iluorsparwhich organic imposek an expensive'added burden for their removal. Fluorspar contains some organic constituents including sulfur compounds as well as sulfide sulfur compounds 'which fluorspar when .treated in the conventional manner produces sulfur dioxide and elemental sulfur carried over as impurities in the hydrogen fluoride product. In the calcination operation -in accordance with the present invention the organic constituents ,arey destroyed and the sultides are decomposed thereby eliminating Athese impurities with the `result that the KVcalcineduorspar upor subsequent treatment with sulfuric .acid produces a mucl purer hydrogen iiuoride.

' The accompanying dnawing Vdiagrammatically illus trates one method of carrying .out the operation. Grounc uorspar is discharged from silo l by a. rotary Valve and delivered to a'weigh feeder 3, or other similar cali brated mechanism, and the material discharged at a con column is a vertical column 6 provided with a `jacket through which hot gases,4 such as combustion gases, ch culate, entering through line Sand discharging throug line 9. To improve heating, the column may be firme externally. lf desired, heating of the column may t accomplished by directing hot gases througha series t internal tubes. At locations where electrical power more economi-cal or more practical, internalheatingfel mentsor Winding on the outside of the heating column oz furnish the heat required. Near the bottom of column is a horizontal distributor grate 11 which supports tl bed 12 of tluidized iluorspar and whicheis perforated j permit passage of fiuidizing gas up through the'be Fluidizing gas, 'such as air or oxygen-containing gas, e ters the bottoni of column 6 through line 13 beneat'hfd tributor'gratell passing upward through bed 12` to mai the sulfuric acid andV wherein some of the particles of solid carriedby the gas 10 drop down to the bed. Any fine dust entrained `in the' duidizing gas is trapped in internal dust collector 14 or in bag filter 1S and drops down to bed 12. After the lluorspar has been calcined at a temperature of 800-1300" per hour of 99.5% H2804 and the reactants maintained in theV furnace at a temperature of about 450 F. Hydrogen fluoride gas evolved as aresult of the reaction was released from the furnace at the rate of 140 pounds per 5 hour and contained minor amounts of SO2 and elemental sulfur, less thanr1.0% and 0.1% respectively. Calcium sulfate, the other product of the reaction was dischargedl from the far end Yof the furnace at vthe rate of v 490 pounds per hour.

Merely by way of comparison, it will be noted that a conventional operation requiring the heavy rails will have a capacity of about 30% less than that produced by the process in accordance with fthe present invention utilizing the same size kiln without heavy rails. Also, the main- F., usually calcinatio'n is completed at that tempenature 15 tenance and operating difficulties are vconsiderably less ,n a, matter of minutesialthough longer times may beiV f :mployed, the calcined uorspa'r is withdrawn lat the bot-. om of column 6 through/a horizontal line 16 from ai :ointz just above distributor grate 11, Normally the and fthe hydrogen fluoride purer as'coimpared with conventional operation. i,

' Although certain preferred embodiments kof theinven-V tion have been disclosed for purpose of illustration, 'it

veight of bed 12 will yexert suiiic'ient pressure to Vforce 20 will be evident that various changes and modifications may luorspar through line 16, but if needed, booster gasesV nay be introduced through line 17 to facilitate carrying he' hot iluorspar lthrough horizontal discharge line 16.

`he booster gas may also be preheated to precludecool- 1g the nuorspar. rom line 16 enters surge hopper 18 wherein the iluo'rf par separates and settlesin a compact mass at the bot- )m of hopper 18 which is preferably insulated to preent loss of heat and the gases pass through rinternal dust scope of the invention'.V i

vWe claim: l. A processfor the manufacture of v*hydrogen fluoride be made therein without departing frornthe spirit and Y The mixture ofY iluorspar kand gasesV 25u/nich comprises calcining iiuorspar in a separate zone at a temperature within theY range of about 800-l300 F.

by passing an o'xygenecontainingV gas through said separate Vzone in direct and intimate contact with a bed of iiuorspar in said vzone to maintain the bed in a Viluidized alleotor 19 and bag nlter 20 toI trap elutriated dust which 30 state, passing the' heated, calcined fluorspar into an exmay be heated to a'ltemperat'ure between about 200- f '0 F., preferably Z50-300 F. (materially higher tem-` 35y the reaction mixture in the reaction zone at atemperature within the rang'efof about 30G-600 F. to effect re- Y actionof the sulfuricacid and iluorspvar to produce liy-A i drogen iiuoride and calcium sulfate, releasing evolved hydrogen iuoride from the reaction zone and discharging :ratures are not desired because theyl create a corrosion 4u calcium sulfate from the reaction zone.

obIem), and then flows through line 26 into furnace 23.

rrternally fired rotary furnace 23 may bev a conventional pe except that heavy rails. are not needed since reacn of the sulfuricacid witha uorspar does not form nps thereby enabling efficient heat transfer and inaased plant capacity.Y The fluorspar' and sulfuricacidv tctants in furnaceZS maintained at a temperature within range of about 3D0-600 F., preferably 400-450? F., Lct to form hydrogen fluoride which is released through A2. A process for theY manufacture of hydrogen fluoride bypassing an oxygen-containing gas through'r said sepaa 45 rate'zone in directV and intimate contact WithY a` bed of fluorspar in said zone to maintain the bed in anuidized Y state, passing the'h'eated, calcined nuorspar into an externally heated rotary kiln, concurrently introducing sulfuric acid having a concen-tnationfof about 9f5-100% charge y2i" andk .calcium sulfate which isV discharged 50' H2SO`4at a temperature within the range of 250e3`00 F.

twn in regulated-amount by means of aweig'h feeder invzan amountin small stoichiometric excess for reaction with'the iiuor'spar intovthe externally heated kiln linV admixture with the iiuorspar, maintaining the reaction rnxl ture in the Vkiln at a temperature'V within theY range of he rate of A300 pounds per hour andthen continuously 55 about 400-450 Eto eifectere'action of the sulfuric acid by a feed screw; into approximately Y'the center of a tical column having a diameter of 1 foot and a height 8 feet. :ributor grate which supports Ya iiuidized column 'of rspar having, a height ofA 5 feet. YA jacket surroundsA column through which not combustion gases are ulated to maintain the iluidized bed at a temperature [000 F. Air at the Vrate of 160 cubic feet per hour passed up through the distributor kgrate and throughr bed of iiuorspar solids inthe colunm to maintain 6 At the bottom of `thecoln'mnis disposed a f Viluidized bed of fluorspar, continuously passing afi'uid'.;l

izing' oxygen-containing gas upwardly through" the-"bed Yto maintain the bedl in a iiuidizedV state, calcining said iluidized bed ofuorspar by heating at a temperature within theV 'rangeof'about'800-1300" F.','zcontinuous`ly withdrawing heated,'calcinedfliuorspar from: the fluidized bed, Vcontinuously passingv saidheated, withdrawn iiuori v spar togetherwith soineiiuidi'zing gas into a'separation 0 zone Vwherein the Agas iss'eparated from the fluorspa' "whichsettlesfiin f the Yseparating'zone inithe formof a Y compact mass, continuously passing said settled, c'alcined n e uorspar 'into an'extern'ally heated reaction zone, con-'fA currently introducing sulfuric V,acid at' a temperature withsflds per hour and therein `was admixed with 380 pounds' '75.i1ithe range ofg, 200-'35.0f- F; in atl least stoiohionretric Y amount for reaction With the uorspar into the externally heated reaction zone in admiXture With the fluorspar, maintaining the reaction mixture in the reaction Zone at a temperature Within the range of about 30G-600 F. to eiect reaction of the sulfuric acid and fluorspar to produce hydrogen fluoride and calcium sulfate, releasing evolved hydrogen uoride from the reaction zone and discharging calcium sulfate from the reaction zone.

4. A process for the manufacture of hydrogen lluoride which comprises continuously feeding uorspar into a uidized bed of uorspar, continuously passing a huidzing oxygen-containing gas upwardly through the bed to maintain the bed in a tluidized state, calcining said liuidized bed of uorspar by heating at a temperature Within the range of about 900-1100 F., continuously Withdrawing heated, calcined uorspar from the uidized bed, continuously introducing gas into the stream of withdrawn iluorspar to aid in its conveyance to a separating zone wherein the `gas is separated from the uorspar which settles in the separating zone in the form of a compact mass, continuously passing said settled calcined uorspar into an externally heated rotary kiln, concurrently introducing sulfuric acid having a concentration of about 95-100% H2564 at a temperature Within the range of 25 0-300" P. in an amount in small stoichiometric excess for reaction with the luorspar into the externally heatedv kiln in admixture With the uorspar, maintaining the reaction mixture in the kiln at a temperature Within the range of `about 40G-450 F. to effect reaction of the sulfuric acid and uorspar to produce hydrogen iluoride and :calcium sulfate, releasing evolved hydrogen uoride from the reaction zone and discharging calcium sulfate from the reaction Zone.

References Cited in the `file of this patent UNITED STATES PATENTS OTHER REFERENCES Perrys Chemical Engineers Handbook, 1941 Ed., pages 32Z-324. McGraw-Hill Book Co., Inc., N.Y.

Othmers book on Fluidizationj pages 212, 221; 1956 Ed., Reinhold Publishing Co., N Y. 

1. A PROCESS FOR THE MANUFACTURE OF HYDROGEN FLUORIDE WHICH COMPRISES CALCINING FLUORSPAR IN A SEPARATE ZONE AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 800-1300*F. BY PASSING AN OXYGEN-CONTAINING GAS THROUGH SAID SEPARATE ZONE IN DIRECT AND INTIMATE CONTACT WITH A BED OF FLUORSPAR IN SAID ZONE TO MAINTAIN THE BED IN A FLUIDIZED STATE, PASSING THE HEATED, CALCINED FLUORSPAR INTO AN EXTERNALLY HEATED SEPARATE REACTION ZONE, CONCURRENTLY INTRODUCING SULFURIC ACID IN AT LEAST STIOCHIOMETRIC AMOUNT FOR REACTION WITH THE FLUORSPAR INTO THE EXTERNALLY HEATED REACTION ZONE IN ADMIXTURE WITH THE FLUORSPAR, MAINTAINING THE REACTION MIXTURE IN THE REACTION ZONE AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 300-600*F. TO EFFECT REACTION OF THE SULFURIC ACID AND FLUORSPAR TO PRODUCE HY- 